1. Field of the Invention
The present invention relates to a blow-by gas refluxing device provided in an engine system having an engine, an intake air passage and a supercharger disposed in the intake air passage. The blow-by gas refluxing device refluxes blow-by gas, which is generated in the engine, to the engine through the intake air passage.
2. Description of the Related Art
It has been known that in an engine installed on an automobile or the like, blow-by gas may be leaked from a combustion chamber to a crankcase through a gap between a piston and a cylinder and may deteriorate engine oil contained in the engine.
A technique relating to a blow-by gas refluxing device that ventilates blow-by gas leaked into a crankcase is reported in Japanese Laid-Open Utility Model Publication No. 4-8711.
The above publication discloses a technique of providing a blow-by gas refluxing device, which has a blow-by gas passage for introducing the blow-by gas from the crankcase to an engine intake air system, a main turbocharger and a sub turbocharger provided in parallel with respect to an engine, intake air and exhaust gas changeover valves that switch between an actuating state and a de-actuating state of the sub turbocharger, and an intake air bypass passage that connects between the downstream side of the sub turbo-charger and the upstream side of the main turbocharger. A discharge outlet on the negative-pressure side of the blow-by passage is connected with the intake air passage on the downstream side of the throttle valve, and the discharge outlet on the atmosphere side of the blow-by gas passage is connected with the intake air bypass passage, thereby introducing the blow-by gas from the crankcase to the intake air system.
However, according to the technique of the above publication, when the pressure on the downstream side of the throttle valve becomes higher than the internal pressure of the crankcase, a problem may be caused that the inside of the crankcase cannot be sufficiently ventilated due to air flow into the blow-by gas passage via the discharge outlet on the negative-pressure side of the blow-by gas passage.
Therefore, there is a need in the art for a blow-by gas refluxing device that can reflux blow-by gas produced in an engine throughout the entire operational range of the engine.